This invention pertains to refractory compositions suitable for forming monolithic refractory structures, and particularly to such compositions containing graphite.
Such "graphitic" refractory compositions are well known (see U.S. Pat. Nos. 1,458,723, 1,458,724 and 3,892,584), as is the fact that the inclusion of graphite and other forms of carbon in a refractory make it "nonwetted" by molten iron, thus reducing the wear of the refractories in such applications as runners for molten iron flowing from a blast furnace. It is also known to add silicon carbide to such compositions to impart increased resistance to oxidation of the carbon. It is also known to add carbon black to such compositions to increase their plasticity, as well as adding further carbon.
However, a problem has arisen with such graphitic refractories which contain water in that they show a loss of workability during storage, particularly when they contain silicon carbide. Such effect is sometimes referred to as "aging". "Workability" is defined by ASTM standard test C-181, wherein a standard shaped specimen of the composition, for example a right cylinder, is subjected to a standard load and the amount of deformation noted; the greater the deformation, the greater the "workability" or "plasticity" of the composition. The reasons for the loss of workability during storage, particularly severe in silicon carbide containing mixes, is not completely understood, but it is believed to be due to free silicon imported into the composition by the silicon carbide reacting with the clay plasticizer in the composition to change the plasticity.
The present invention is directed to a solution of this problem of an unacceptable loss of workability or plasticity in these graphitic compositions during storage.